Internal-combustion engines, such as those in most automobiles, are typically designed with a plurality of reciprocating pistons, each actuated by a connecting rod pivotably connected to the pistons, and eccentrically and rotatably connected to a crankshaft, which ties the plurality of pistons together, and determines their relative position within the engine during the engine cycle. The crankshaft is generally held within a block portion of the engine, while the pistons reciprocatingly slide within respective cylinder bores within an upper portion of the engine block. Combustion occurs within the combustion chamber of each cylinder, defined between the top of the piston, the wall of the cylinder bore, and the head of the cylinder.
In reciprocating internal combustion engines, the combustion ratio (r) is the maximum volume of each cylinder's combustion chamber (Vmax) in relation to the minimum volume of each cylinder's combustion chamber (Vmin), expressed either as a ratio or as the quotient of the two volumes. The maximum cylinder volume is calculated when the piston is positioned at the bottom of its range—at bottom dead center (BDC), with the minimum cylinder volume being calculated when the piston is positioned at the top of its range—top dead center (TDC). The distance traveled between TDC and BDC positions is termed the “stroke” of the piston. Even at the TDC position, a clearance volume typically remains above the piston. The clearance volume is the remaining volume of the cylinder, when the piston is at the TDC position (Vmin). In summary, the compression ratio (r) is defined as shown below.
  r  =                    V        max                    V        min              =                  V        BDC                    V        TDC            
The compression ratio (r) affects various aspects of engine performance, and depending on the compression ratio, power output and/or fuel efficiency and/or engine noise and vibrations, as well as other combustion characteristics can be modified. All production engines have a fixed compression ratio, which is limited by occurrence of “knock,” due to premature fuel combustion, under full-load operation. Under partial-load operation the engine can be satisfactorily run at a higher compression ratio for higher thermal efficiency, lower fuel consumption and reduced emissions. However, lower compression ratios necessitated by full-load operation characteristics limits an engine from achieving any of the benefits of a higher compression ratio—namely higher efficiency, lower fuel consumption and reduced emissions under partial-loads.
Systems have been developed previously for adjusting compression ratios of internal combustion engines, many of which are excessively complicated, resulting in increased weight and cost, and reduced reliability. Some of such systems rely on variable cylinder volume, such as by repositioning the cylinder head, and thus the cylinders, with respect to the crankshaft and piston TDC (and BDC) positions. Other systems rely on variability of the piston top dead center. Some of such systems function by moving the crankshaft, and thus the TDC (and BDC) positions with respect to the cylinders, others function by adjusting connecting rod position with respect to the crankshaft by adjusting the height dimension of the piston itself, for example.
The above-described proposed systems and methods have generally proven unworkable due to their complexity, cost and unreliability. Therefore, a continued need exists for systems to vary compression ratios to achieve efficiency in fuel economy, that is simple, reliable and relatively inexpensive. The present invention provides a solution for these continued needs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.